"A DiskVaccuum For Obsolete Disk Formats"

On 01/12/2014 06:36 PM, Chris Pye wrote: Don't let the term "double density" confuse you--basically the coating's the same for all 8" floppies. What differs is the position of the index aperture in the jacket. Worst case, you might need to punch a hole in the jacket in the correct position. The thing about "double density" (MFM) and "single density" (FM) is that the maximum number of flux transitions per unit distance on a track is exactly the same in both cases. In FM, there is an explicit clock pulse accompanying every data pulse. In MFM, the number of pulses are reduced, as it's possible to infer a clock pulse, so long as a set maximum space between pulses is observed. So it comes down to what the drive thinks it is--and that's specified by the position of the index aperture. Simple and reliable. FWIW, it's also possible, using the right drive to use hard-sectored media as soft-sectored. That is, you can jumper many 8" drives to separate the index pulse from the sector pulses and place only the index pulse on the INDEX output. In most cases, you can use soft-sectored media without re-jumpering the drive. So don't throw those 8" floppies out! --Chuck